Iran's Supreme Leader Ayatollah Ali Khamenei has reasserted his country's right to produce nuclear energy.
Mr Khamenei appearance confirms official denials of his death
Speaking to mark a Shia religious holiday, the ayatollah also warned Arab countries against siding with Britain and America against Iran.
The BBC's Frances Harrison, in Tehran, says it is his first appearance since false rumours of his death.
Iran denies it is seeking nuclear arms, saying its wants to enrich uranium only for peaceful nuclear energy.
Our correspondent says the supreme leader showed no concern about the recent UN resolution imposing sanctions on Iran's nuclear programme.
Instead, he endorsed the rhetoric of the hardline President Mahmoud Ahmadinejad who has repeatedly stressed Iran will not give into international pressure on the nuclear issue.
Meanwhile, the deputy commander of Iran's Islamic militia force, the Basij, has reportedly said that Iran could pressure the west by blocking oil shipments through the straits of Hormuz.
He said more than 40% of the world's energy passes through the narrow sea lane which Iran dominated.